Flush,or drain tranny fluid


#1

Opinions on flushing,or draining my GMC sierra pick-up tranny fluid. Manual says “service” whatever that means.

My mechanic says flush.


#2

I am a member of the pan drop, replace gasket, filter change, drain and refill crowd – no flushes unless the fluid is extraordinarily dark or black. If this is routine, normal maintenance (you didn’t indicate mileage on truck), I would not flush. Mechanic likes flush because it is fast and easy. Seems to be a good money-maker. Only problem is filter doesn’t get changed out without the pan drop.


#3

If you have been having the fluid and filter changed as per the maintenance schedule and the fluid isn’t burnt or contaminated, that is all you need. You only end up changing about 1/3 of the fluid this way, but that is usually sufficient if you do it at the proper frequency.

If you do any towing or heavy hauling, change the fluid and filter every 25K - 30K miles, and consider adding an auxiliary transmission cooler.


#4

Just to make sure you understand, flush or drain is an extremely controversial topic, with many people on both sides. Both posters are correct again. Draining at the stated mileage in the manual is usually sufficient. But, you will encounter many mechanics who swear your tranny will fail tomorrow if you do not pay them large amounts of money to flush. It usually isn’t true, but they will swear it.

Some people believe an older transmission is likely to fail because of stuff knocked loose by flushing. Others say it was going to fail anyhow from lack of regular draining. As the old saying goes, you pays your money and you takes your choice.

I pull the plug whenever I think of it, let three quarts run out, and put the plug back in and add three quarts of synthetic fluid. My sienna has towing package so there is plenty of cooling. I do not urge anyone to imitate me; it is a personal decision, which is what you must make as well. In the end, it is your transmission and the important thing is to get new fluid in there regularly.


#5

There is one thing everyone will agree on. You need to service the transmission fluid at least as often as listed in the owner’s manual. Most will agree that it should be no less than about 50,000 miles.

Flushing has some apparent advantages as it will change more of the fluid and is easier (not always cheaper). It has the disadvantage in that it usually does not include dropping the pan and cleaning what may be on the bottom and cleaning the filter, both very important in my opinion.

For those who say don’t do at all (there are a few, very few) I would say that they say this because they or someone they had was having some indication of a transmission problem and they had the fluid serviced. It then failed in a few days or months. Of course the real reason it failed was the same reason they had it serviced, it was already toast and changing fluid would not repair the already existing damage.

Good Luck


#6

In the olden days most cars were RWD (right wheel drive). They all had torque converters that could be drained via an accessible drain plug and a transmission with pan that you could remove to drain the trans and change the filter. Now, even some RWD vehicles don’t have a TC drain plug any more. The only reasonable way to service them in a shop is to put them on a machine that does a fluid exchange because it takes little time. At home, you can pump the fluid out by removing the cooler lines something like this:

http://www.crownvic.net/tech/transservice.htm


#7

If you are following the service schedule in your owners manual, then first let me say way “good job”. As for your question, a drain and refill is all that is needed. The engineers set up this schedule with the fact in mind that a drain and fill does not replace all the transmission fluid. If it did, they would have extended to drain period.

This goes for all the other fluids too, coolant, oil etc. Some shops want to sell you a flush for everything when a drain and fill is all that is needed. The only fluid that needs to be flushed on a regular basis is the brake fluid. You flush it because you don’t want to introduce air into the system.


#8

I think the word “flush” scares the crap out of anyone who’ve never used a “Transmission Fluid Exchange Machine”.

You remove one of the transmission cooling lines from the radiator. You connect one hose of the machine to the cooling line and other hose to the radiator. So now the machine is in the loop. You fill a clear plastic cylinder in the machine with fresh tranny fluid. At the bottom of this clear plastic cylinder is a piston. You start the engine and shift the transmission though it’s gears. The pump within the transmission forces the old tranny fluid into the clear cylinder in the machine where it starts pushing up on the piston at the bottom. As the piston is forced up in the clear cylinder, the fresh tranny fluid is sent back to the transmission. You continue to do this until the fluid coming out the transmission is the same color as the fluid going in. And sometimes this takes many quarts of fluid before the colors are the same. Hence the price. So I don’t see where damage can occur when using one of these machines.

Transmission fluid is just 10W oil with the proper additives. And just like engine oil, it breaks down over time. So it should be treated like you would with your engine oil. Change it all. Not just 30%.

But I do agree, have the pan dropped, inspected, cleaned, and change/clean the filter when doing a tranny fluid exchange.

Tester


#9

I know that for my car, the 30 K “transmission service” is assumed to replace nearly all the fluid whether that is with a machine that exchanges most of the fluid or by draining the TC and trans and refilling. You could do that by draining the trans pan and refilling repeatedly. It would take nearly 30 quarts of fluid to get down to 6% residual fluid if I can get half of it out.